Propane fractionation of reduced crude oil with recycle of heavier bottoms



Aug. 12, 1952 B. c. BENEDICT 2,606,859

PROPANE FRACTIONATION OF REDUCED CRUDE OIL WITH RECYCLE OF HEAVIER BOTTOMS 2 SHEETS-SHEET 1 Filed Feb. 28. 1949 1N VEN TOR.

AT TOR/V575 Aug. 12, 1952 B. c. BENEDICT 2,606,859

PROPANE FRACTIONATION OF REDUCED CRUDE OIL WITH RECYCLE OF HEAVIER BOTTOMS,

2 SHEETS-SHEET 2 Filed Feb. 28, 1949 INVENTOR. B. C. BENEDICT F/G. Z

A TTORNEVS Patented Aug. 12, 1952 PROPANE FRAGTIONATION F REDUCED CRUDE 011. WITH RECYCLE 0F HEAVIER BOTTOMS Bruce C. Benedict, Bartlesville, 0kla.,

asslgnor to Phillips Petroleum Company, a corporation: of

Delaware Application February 28, 1949, Serial No. 78,724"

14 Claims. 1

This invention relates to propane-fractionation of lubricating oil stocks. In one of its more specific aspects it relates to a method for the treatment of low asphalt-containing lubricating oil stocks for the separation and recovery of the lubricating oil fractions. In a still more specific aspect it relates to a process for the separation and recovery of lubricating oil fractions from crude lubricating oil stocks containing some asphaltic material by fractionation with liquid propane wherein asphaltic constituents are not precipitated and caked in the treating apparatus.

The asphalt content ofa crude oil may conveniently be defined as the per cent of residue from the vacuum distillationof a crude oil having a maximum A. S. T. M. D243-36 penetration of 100 at 77 F. For Oklahoma City crude oils this asphaltic residue constitutes about 2% by weight of the crude oil. I

.By the term low-asphalt crude oil I mean crude oils containing a maximum of about 5% asphalt by weight as determined by theabove mentioned A." S. T. M. method.' Such a lowasphalt containing crude oil may be distinguished from conventional asphaltic crude oils such as California crudes which contain from 12% to 65% asphalt, and from Wyoming and Arkansas crude oils which contain about 30% asphalt.

Deasphalting petroleum oils and moreparticularly reduced crude oils from which distillate lubricating oil fractions have been removed is old in the art. Such operations are usually carried out at temperatures between about 70 and 140 F. to take advantag of. the precipitating action of propane on the heavy asphaltic constituents of the oil. It has also been recognized for many years that a fractionating effect can be obtained with propane-oil mixtures at temperatures ranging from about 140 F. up t the critical of propane. Utilizing the unique properties of liquid propane whereby increasing temperatures result in progressive rejection of hydrocarbons in such a manner that the higher molecular weight components and the more aromatic and naphthenic components are separated first and the lighter components and more paraifinic hydrocarbons last, a combination of low temperature distillation and solvent extraction is achieved. However, due to the difliculties involved in working at high pressures and in close proximity to the critical temperature of propane, commercial exploitation was unknown until quite recently.

It has been found, however, that some lowv asphalt-content reduced crude lubricating oil may be fractionated continuously by liquid propane under high pressure and at a relatively high temperature, while other such crude oil stocks can be fractionated only for very short periods of time. In this'latter case it has been found that the fractionating equipment became plugged with a deposit of asphaltic material. This asphaltic material has apparently been precipitated from the oil upon contact with the high temperature propane. It should be mentioned that the oils in question Were low asphalt-containing oils and did not differ significantly from each other in total asphalt content, as conventionally determined. Why some caused plugging trouble and others did not is not clearly understood.

An object of my invention is to devise a process in which a low asphalt-containing reduced crude lubricating oil stock is fractionated for the separation and recovery of lubricating oil constituents. Another object ofmy invention is to devise a method for the separation and recovery of lubricating oil fractions from such low asphalt-content crude lubricating oil stocks by fractionation with liquid propane without the formation of hard asphaltic deposits in the oil fractionation apparatus. Still another object of my invention is to devise a continuous process for the removal and production of lubricating oil fractions by fractionation with liquid propane from low asphalt-containing reduced crude oil stocks suitable for the manufacture of lubricating oils, wherein the asphaltic constituents are maintained in such a form that they do not adhere as a hard mass to the fractionation equipment. Still other objects and advantages of the process of my invention will be obvious to those skilled in the art upon reading the following disclosure. which, taken with the attached drawing, forms a part of this specification.

In preparing to apply the above mentioned unique properties of liquid propane to actual commercial fractionation of certain grades of lubricating oils from residual stocks, ahitherto unrecognized problem was encountered. Upon fractionating some Mid-Continent reduced crude lubricating oil stocks with liquid propane in a countercurrent contacting tower at a propaneto-oil volume ratio of about 7:1 with temperatures ranging from about 195 F. at the top to about F. at the bottom of the tower, an SAE 40 oil was continuously separated in the overhead product. On the other hand, when a very similar Mid-Continent reduced crude lubricating oil stock was charged to the process under the sam operating conditions a similar fraction of lubricating oil was initially obtained, but the column rapidly filled with a hard .asphaltic material in the stripping section thereby making continuous operation impossible. In this second case, a third phase, that is, a semi-fluid asphaltic phase was apparently produced along with a propane-rich light oil fraction and an oil-rich solution of propane in heavy oil. Upon contacting the charge oil with liquid propane this third phase when first formed was suihciently fluid to flow nearly to the bottom of the column before the ascending propane had washed it sufficiently to cause it to set to a hard cake. Upon continued operation, this cake builds up in the column until complete closure of the column occurs. Why one low asphalt-containing oil should deposit its asphalt while another low asphalt-containing oil does not when the two oils contain similar amounts of asphalt is not definitely known.

In a study of three well known Mid-Continent crude oils which have long been recognized as excellent sources of lubricating oil stocks, hard deposits were formed when treating two of these stocks with liquid propane while the third was fractionated with propane continuously and without difliculty. It has als been found that some West Texas".loweasphaltecontent reduced crude oils can be continuously fractionated with propane while others cannot. Itis therefore realized that propane fractionation cannot be universally applied to all so-called low-asphalt reduced crude lubricating oil stocks.

I have now discovered that on cause of the deposition of asphaltic material from some low asphalt-containing crude oils when undergoing propane fractionation is a deficiency of the heavy oil, which oil acts in the stripping ection oi the fractionator to prevent the deposition of a hard asphalt. Th present invention overcomes this difiiculty by utilizing a recycle of the heavy oils from the bottom of a second propane fractionating column which has for its charge the bottoms from a first propane fractionating'column. The bottoms from the second column represent a high concentration of the very heavy oils originally present in the crude oil and the recycling of these bottoms into the stripping section of the first or primary fractionating column increases the proportion of heavy oils sufiiciently to prevent the formation and precipitation of the heavy asphaltic phase which plugs the column. a

In the drawing Figure 1 represents, diagrammatically, a form of apparatus in which to practice the process of one embodiment of my invention.

Figure 2 represents-, diagrammatically, a simi lar form of apparatus in which to practice the process of a second embodiment of my invention.

Referring now to th drawing, and specifically to Figure 1, a fractionating column I is equipped with several pipe connections for inlet of materials entering the process and for outlet of materials leaving this column. Pipes 2 and i9 enter the column at a point somewhat above the midpoint of the column, while line 3 enters the column at a point near its base. Pipe 7 provides for withdrawal of overhead product while pipe 8 permits removal of the bottoms. A second fractionator column 2| is similar in all respects to column I, this second fractionator having also a charge oil inlet pipe 22, a pipe 23 near the bottom, an overhead product withdrawal pipe 21 and a bottoms withdrawal pipe 23-. Column l is provided with a heating coil 9- in the top of the column while column 2| also has a coil 29 for heating purposes.

In the operation of my process a reduced crude oil having an initial boiling point of about 850 F.

is prepared by distillation to remove the SAE and stocks. This reduced crude oil containing all crude oil components of SAE 30 and heavier is then fractionated by means of propane to produce an SAE so to 50 overhead product, an SAE 70 overheadproduct and an asphalt-containing heavy oil bottoms product.

This prepared reduced crude oil is charged through the line 2 into the propane fractionating column i which has previously been filled with liquid propane under a pressure of about 640 pounds per square inch gauge. Th oil feed inlet temperature may vary from about 180 to 200 F. and the contents of the fractionating tower at the feed inlet point is maintained approximately within these temperature limits. Upon contacting the propane within the column at the feed point some of the charge oil dissolves to form a propane-rich phas containing dissolved oil, while some of the charge remains undissolved and tends to settle in the column as an oil-rich phase insoluble in liquid propane. This oil-rich phase, of course, contains some dissolved propane which is acquired during its descent from the feed point to the bottom of the tower. This oil-rich phase accumulates in the bottom of the tower and a sufiicient quantity is permitted to remain in the tower so that there will be an appreciable depth of oil as indicated by reference numeral 5. Reference numeral i indicates the propane-rich phase which remains above the oil-rich phase, the two phases meeting at the interface 6. Pro pane is charged into the column through the line 3 and this propane passes upward through the oilrich phase 5 and strips from this phase oily materials which are soluble in the propane. Upon reaching the interface 6 this propane then enters the propane-rich phase in which it, of course, is completely soluble. The propane-rich phase then ascends through the fractionator and finally reaches the top of the tower. This propane charge stock-is introduced into the bottom of the tower at a temperature between thev approximate limits of and F. and the bottom of the fractionator is maintained at approximately a temperature between these limits. A heating fluid is passed through the heat exchanger 9 in the top of the tower so as to maintain the propane solutionin the top of this fractionator at a temperature between'the approximate limits of 190 and 210 F; It will be noted that points higher up the tower are maintained at higher temperatures than lower points in the tower since oils ar less soluble in propane at higher temperatures.

The propane passing through the oil-rich phase 5 becomes substantially saturated with oily constituents at the temperature of the bottom of the iractionator. This saturated propane solution then on rising from the interface 6 toward the charge oil inlet point increases in temperature somewhat and this increase in temperature causes a precipitation of the more aromatic and naphthenic and heavier components of the propane solution so that additional oil-rich phase is produced and this additional oil-rich phase, due to its difference of specific gravity from the suspending solution, tends to settle downward and on settling is washed by the ascending current of propane-oil solution.

In the upper section of the tower, the temperature is increased from the feed point to the top which ismaintained at the highest temperature of any point in the tower. In this upper section additional heavy oil is precipitated due to its decreased solubility at th higher temperatures and this heavy precipitated oil also settles downward through the ascending propane solution and this oil is washed of its lighter oil constituents by the propane. By maintaining the temperature at the top of vessel within the limits of about 190 to 210 F. an SAE 40 to 50 grade lubricating oil stock remains in solution in the propane and this material is then passed from the fractionator through the line i to a propane separation apparatus, not shown. In this propane separation apparatus, the propane and the oily constituents may be separated by fractionation or any means desired, and the oil recovered therefrom may be passed to a subsequent treating step or to storage, as desired. I

The oil-rich phase accumulating in the bottom of 'fractionator I is removed therefrom through the line 8 and this material is then passed as charge stock through exchanger 33 and line 22 into the second propane fractionating column. This column has previously been filled with liquid propane under a pressure of about 460 pounds per square inch gauge. Heating fluid is passed through the heat exchanger coil 29 in the top of the vessel 2| to maintain the propane solution at that point at a temperature between the approximate limits of 140 to 160 F. The propane to this column is added through line 23 at a temperature between the approximate limits of 130 to 150F. The heat exchanger 33 may in this case be a cooler so that the oil-rich phase removed from fractionator at a temperature between 170 and 190 F. may be cooled to a desirable charge temperature for introduction into vessel 2| so that the temperature at the charge oil inlet point may be held at a value somewhere between the bottom column and the top column temperatures. If the bottom column temperature is, for example, 130 F. and the top temperature 140 F. then the oil from line 22 should be at such a temperature that when mixing with the rising propane solution the average temperature at the charge oil inlet point will be about 135 F. In this manner a substantially uniform temperature gradient may be maintained throughout the length of the column. Sufficient propane is introduced into column I through line 3 that the propane-to-charge stock oil ratio may be between the approximate limits of 6:1 and 10:1.

The oil-rich phase withdrawn through line 8 from the bottom of column I contains only a relatively small proportion of propane and accordingly only little propane reaches column 2| from this source. Suflicient liquid propane is then introduced into column 2| through the inlet line 23 to maintain the ratio of propane-to-oil in column 2| between the limits of about 6:1 to 14:1. This propane entering column 2| through line 23 passes upward through the oil-rich phase 25 and in so doing strips propane-soluble oils from this phase. By the time the propane reaches the interface 26 the propane is substantially saturated with oils so that the propane-rich solution in the vicinity of the interface 26 is for all practical purposes a saturated solution of oil in propane. This solution then upon rising in the tower 2| becomes heated and this heating reduces the solubility of the heavier oily constituents and of the more asphaltic and aromatic constituents so that these materials then become precipitated as an insoluble. oil phase suspended in the propane solution. At points below the oil feed inlet point this newly formed oily precipitate may unite physically with the oily material from the ,charge oil which is insoluble inthe propane solution at the conditions at the charge 011 inlet point. Thus, there exists in this section of the tower a relatively highco'ncentration of heavy oily material and under these conditions fasphalt is not precipitated but remains in solution in this heavy oil. This asphalt-containing heavy oilthen aceumulates in thebottom of the tower as the oilr-ichfphase 2.5 and thisinaterial is removed then through the'bottoms draw-off line 28. I have found by dividing the stream of oil-rich phase passing through line 28' and passing a portion through line 3|] and under influence of pump 3| on throughline I0 into the primary fractionating column at' about the crude oil charge inlet point, that Iiam able to maintain a, suificientlyhigh concentration of heavy oilymaterial in the section of vessel I. below the feed pointso that the hard asphaltic material is not precipitated. The oil flowing through line 28 of Figure l is divided so that from 10'per cent to 50 per cent of this oilrich phase is passed through line 30 under the influence of pump 3| and on through line l0 into column at about theoil feed point.

By maintaining the temperatures in column 2| somewhere between the above given temperature limits the propane solution leaving the column through overhead line 21 contains oily materials having an average'SAE grade of'about 70. This propane solution may then be passed to an oil recovery system not shown, in which the oil and propane are separated and from which the oil may be passed to further treating steps or to storage, as desired. The recovered propane from the overhead product of column 2| and the propane from the overhead product from column I are, of course, recycled to the system. It is not necessary in both of these columns to maintain the pressures at the exact value given, the main point, of course, being that the column should be operated under sufficient pressure to maintain the propane as a liquid or dense phase under all temperature conditions. As a safety factor, it may be advisable to operate these columns at a pressure about 40 to 50 pounds per square inch gauge greater than the vapor pressure of propane at the highest temperature in the columns.

The portion of the oil-rich phase from line 28 which is not recycled to the feed point of column I may be withdrawn from the system through line 32 and passed to a propane recovery system in which a relatively small amount of dissolved propane is recovered from the heavy oil. However, this .oil-rich phase withdrawn through line 32 may, if desired, be subjected to fractionation in still another propane column operated under such conditions as to produce, for example, an overhead oil of SAE to SAE 250 grade. After the system has been operated sufficiently long to acquire an equilibrium condition the amount of heavy oil inthe oil phase removed from the system through line 32 is equal to the heavy oil content charged to the system through line 2. In this manner the oil recycle is kept constant. In order to facilitate mixing of the charge stock to column with the heavy oil recycled from column 2| to column the reduced crude charge stock may be introduced into line I0 through a branch inlet, not shown. This feature is subsequently discussed in connection with Figure 2.

Specific examples As an example to show that addition of heavy oils will change the phase relationships sufficiently to prevent asphalt deposition, tests were made on topped crude oils and mixtures of topped crude oils and bottoms from a propane fractionation step inwhich SAE 70 oil was taken overhead. The primary fractionation step in'which asphalt commonly precipitates was so operated as to take an SAE 50' oil overhead.

Tests were made in'a single stage propane fractionation operation in which feed plate conditions of a countercurrent column were approximated and the resulting asphalt deposited under equilibrium conditions was quantitatively measured. The reduced crude oil and propane were charged into a rocking autoclave of one liter capacity and the conditions of temperature and pressure were so controlled that during the test an extract was made atthe conditions existing at the pint of crude oil inlet to a countercurrent fractionator. At'the end of approximately one hour under these test conditions in which the autoclave was continuously rocked, the test was stopped and nitrogen gas was used to displace the contents through an eduction tube which extends to the bottom of the autoclave. Test pressure and temperature were maintained until the sample was completely removed. Following sample removal, the interior of the autoclave was visually inspected for asphalt deposits. The autoclave was then washed with benzene and the washings collected. The benzene was evaporated from the washings and the residue was weighed. The asphalt content of this residue was deter- 8 yielded an appreciable amount of asphalt in th autoclave. This oil gave 0.91% of deposited asphalt based on the weight of oil charged to the autoclave. When 50% of a Burbank bottoms from an SAE 70 propane fractionation were mixed with 50% of Burbank reduced crude oil and tested in the autoclave no visual deposition of asphalt could be found. The hexane insoluble material amounted to only 0.05% based on the Burbank reduced crude oil charge in this test. When 75% of Burbank reduced crude oil was mixed with 25% Burbank bottoms from an SAE '70 propane fractionator and the mixture tested in the autoclave, only a slight asphalt deposit could be seen in the autoclave. Hexane insoluble material was 0.13%. Such mixtures of Burbank reduced crude with the Burbank bottoms could be charged to a primary propane fractionator, taking a so to 50 oil overhead in continuous operation without asphalt deposition in the section of the fractionator below the feed point.

The apparatus of Figure 2 used for practicing the process of a second embodiment of my invention is similar in many respects to the apparatus illustrated iii-Figure 1. This apparatus of Figure 2 includes fractionating columns 4! and 46. To column A1 are connected an overhead product line 44, a bottoms withdrawal line 45, a line 43 for introduction of liquid propane, and a line for introduction of charge and recycle oils. To column 46 are connected an overhead product mined as material insoluble in hexane. The folwithdrawal line ll, a bottoms withdrawalline 60, lowing test results were obtained. a propane inlet line 18 and a feed inlet line 35.

Autoclave washings fi FWD?! Percent Visual Obser ation g 011mm Total on, Asphalt, Asphalt Grams Grams Grams Chg. Basis West Edmond (Okla) Reduced Crude 040 180 6.421 0. 86 0.76 0.03 0. 02 N o Asphalt.

which did not Plug a Column. Andector (Texas) Reduced Crude which 640 180 6. 1:1 1.67 1.55 0.02 0.02 Do.

did not Plug a Column. 7 Oklahoma City Reduced Crude which 640 180 6.411 2. 44 1.97 0.39 0.30 Asphalt Present.

plugged aColumn. Bigbonk Reduced Crude which Plugged a 640 180 6. 4:1 4. 53 3. 1G 1. l8 0. 91 Do. olumn. 50% Burbank Reduced Crude 50% Bur- 640 180 6.411 2.12 2.05 0.06 0.05 No Asphalt.

bank Bottoms from SAE Run. Burbank Reduced Crude 25% Bur- 640 6.4:1 3.16 2.85 0.17 0.13 Small Amount of bank Bottoms from SAE 70 Run. Asphalt.

All of the above tests were carried outat a temperature of 180 under pressure of 640 pounds per square inch gauge and at a propane to oil ratio of 6.4:1. In the first test a West Edmond, Oklahoma, reduced crude oil was tested. This crude oil, when tested in a continuously operated pilot plant propane fractionation column, did not give an asphalt deposit at points below the feed point. When the autoclave was operated under feed plate conditions for removal of an SAE 40 to 50 overhead lube stock it will be noted that this crude oil also gave no asphalt deposition on the interior surface of the autoclave. Similarly, an Andector, Texas, reduced crude oil which did not plug with asphalt a pilot plant column, also did not give asphalt deposition in the autoclave. An Oklahoma City reduced crude oil sample which did. give asphalt deposition and plugging of a pilot plant column also gave some deposited asphalt in the autoclave. The test results of the table indicate that 0.30% of asphalt was deposited, based on the oil charged to the autoclave. A Burbank, Oklahoma, reduced crude oil which also plugged a pilot plant fractionation column Both columns are provided with slats or bafiles for promotion of more efiicient liquid-liquid contacting. Heating coils 52 and 53 are situated in the upper portion of columns 01 and 46, respectively. A pipe 50 carries a pump 5! and connects pipes 60 and 40. Pipe 05 is provided with a heat exchanger 61 disposed in close proximity to column 35. A line 09 connects also with pipe 00 for transfer of bottoms from column it to storage or to other disposal, not shown. Line 42 is connected with the feed inl-et line 00 for supply of raw feed stock, from a source, not shown.

For operation both columns are filled with liquid propane at desired pressures and temperatures and then oil feed stock is introduced through lines 42 and 40 into column ll. After operation has progressed for a suflicient period of time that the system is in operational equilibrium column 41 is filled with two liquid phase, the lower liquid phase 55 being an oil-rich phase containing some propane in solution and an upper phasefit being liquid propane containing' some dissolved oil. Reference numeral 54 refers to the liquid-liquid interface between these 7 the point of feed inlet as represented by pipe 40.

It is preferred that this interface be maintained from 2 to 6 feet above the feed inlet point.

In column 46 are also maintained a propane phase 59 containing some dissolved oil and an oilrich phase 58 containing some dissolved propane. Interface '1 represents a liquid-liquid interface between these two phases. This-interface in column 46, in operation, is maintained at a point well down the column, preferably a short distance above the propane inlet line 48; V

In the operation of the process embodiment using the apparatus of Figure 2 the oil feed stock to be fractionated passes through line 42 from a source, not shown, on through thefeedinlet 40 into the upper portion of the'oil-rieh phase 55. Oil-rich phase from column4| is passed through line 45 to a midpoint of tower 46 as feed stock and therein forms an oil-rich phase 58. As in the process embodiment of Figure 1, the oil-rich phase 58 is withdrawn from column 46 and divided into two portions. One portion passes through line 56 under influence or, pump 5| into the inlet, 40. In this inlet line 40'the cycle oilrich phase and the raw feed stock are mixed and it is intended that mixing at this point be complete so that a homogeneous oil feed stock enters column 4|. A mixing orifice, eductor or other mixing means may be provided if desired.

In order that stripping of propane-soluble oils may be complete or substantially complete, I prefer to" maintain a' constant temperature throughout the oilrich phase. in column 4|. Beginning at the interface 54, I prefer to maintain a temperature gradient throughout the propane-rich. phase 56, the top .ofthis phase being at a highe temperature than that of the interface. The increasingly higher temperatures in the propane ,phase 56 cause precipitation of the more aromatic, naphthenic and higher molecular weight. parafiinic materials from* solution. As examples of temperature conditions, the top of the column 4| in the region of the heater 52 may be maintained at about 200 F. while the temperature of the propane-rich phasedecreases on passing downward toa minimum of about 190 F. at the interface 54. The oil-rich phase is then maintained at about this temperature. The liquid propane added through line 43 is also introduced at about 190 F.

The top of column 4| of Figure 2 is maintained between the temperature limits of 190 and 210 the feed point between the limits of 180 and 195 F. and the bottom is maintained at about the feed point temperature. The top of the column 46 is maintained within the temperature limitsof 140 to 160 F., the bottom between the limits of 130 to 150 F. The top of the secondary zone 4|-5 is always maintained at a higher temperature than the bottom thereof. Propane is added through line 48'between the volume limits of 6:1 and; 10:1, of propane to oil charge stock, and propane is added through line 43 to column 4| between the Volume limits of 6:1 and 10:1 of propane to oil feed.

The conditions of operation of the secondary column 46 are substantially the same as for column 2| of Figure 1. Columns 2| and 46 may, of course, also be operated with the phase interface above the feed entry, although this is ordinarily not done, a r

10 Specific example A reduced-crude oil stock ofabout 850 F. initial boiling point. is prepared by distillation to remove SAE 10 and SAE 20 stocks. This said reduced crude oil containing all. crude componentsheavier than SAE 20oil-is then fractionated by means of-propanegto produce'SAE 50'andSAE '70stocks as. overhead productsand a. final asphalt product according to the'l following sequence of operations..-

The reduced crudeIoilis ohargedinto the propane fractionating column 4|. through oil feed lines 42 and 40.! The oil-feedltemperature is about 190. F., the column top temperature about 200 F. and the'bottom temperature about 190 F. The. column pressure'isIabout' 640, pounds per square inch gage. A. volume,..of propane equal to '7 to 8 times the volu'm'e'of ollcharg'ed is introduced through line 43 ne'arthe'bottom of the column. The propane. column is so operated that the continuousphase,atthepointof oil feed entry is theoil-richphase 55. The oil-feed entryis near the midpoint of the column. The points of oil entry and propane entry should be so separated that the oil-rich phase may be well stripped of light oils by the "propane rising up through .the column. A temperature gradient of about 10 'F. .is maintained,for fractionating purposes between the oil feed and the tower top. The stripping section, from the oilinlet to the bottom offthe column, is maintained at a constant temperature to j facilitate stripping. The overhead fraction from this column comprises a propane solution of SAE' 40 to. SAE 50 oil depending upon the operating variables of temperature, pressure, and the ratio of propane to oil and is withdrawn throughline 44. The bottom product which consists ofithe propaneinsolublephase forms the oil-rich phase which is withdrawn from the column. through line 45. The .rate of withdrawal of this phase is adjusted to hold the interface at a' constant level in the column and at. a point above theoil feed entry.

The oil-richphase'from column 4! is then charged into' another propane fractionating,

column 4'6 for fractionation into an SAE 70 fraction. This second column 46 is operated. at lower temperatures and pressure than the first column. Forthe preparation of a the SAE 70 'fraction, the column pressure is about 460 pounds per square inch gage. 'Additional propane is added through line 48. The oil feed temperature is about F. with the top and bottom tower temperatures at F. and 140 F respectively. The propane-to-oil ratio is about 8 in column 46. A portion of the bottom product from this column, which is the oil-rich phase and contains veryv heavyoils and resins, is then recycled through 'line 50 into propane fractionating' column 4 The point of introduction of the oil is located below the interface 54. The-amount of oilfphase which is recycled depends, of course, upon'the 1stockjbeing treated, and may vary between the limits of 10% and 50%- or the oil -irich phase withdrawn'through' line 60. The remaining bottoms which arenot recycled maybe drawn off through line 49 and passed to storage, or further fractionated into SAE 70 orSAE 250 oil stocks, as desired;-

The increased concentration of heavy oils and resins in the stripping section of column 4| is suflicient tochange the phase relationships and prevent the formation of the hard asphaltic phase which plugs the-column. I

Auxiliary apparatus such as pumps, valves,

temperature measuring andindicating devices, pressure measuring and indicating devices, controls and flow meters, and the like, are not shown or described hereinfor purposes of simplicity. The installation and operation of such auxiliary equipment is well understood by those skilled in the art. Materials of construction for the apparatus as herein described need not be specific materials since ordinarily corrosion problems are not encountered. The equipment must, however, be so designed'and constructed as to withstand the relatively high operating pressures necessitated to keep the propane in the liquid phase at all times. It will be obvious to those skilled in the art that the conditions of operation and other alterations and variations may be made and yet remain within the intended spirit and scope of the invention.

Having disclosed my invention, I claim:

1. In the propane fractionation of lubricating oil constituents from low asphalt-content reduced crude lubricating oil stocks with liquid propane wherein solid asphaltic materials precipitates upon initial contact with the propaneand adheres to and plugs the fractionating apparatus in the region adjacent and below the raw feed entry point, a process for continuously carrying out this fractionationoperation without precipitating said asphalt and plugging said apparatus comprising maintaining a body of liquid propane containing dissolved oil in a first treating zone, maintaining a body of an oil phase rich in asphalt below said. body of propane containing dissolved oil in said zone, said bodies meeting at a common interface, introducing a stream of liqdid propane into said body of oil phase rich in asphalt and a stream of said asphalt-containing lubricating oil stock-into said body of liquid propane containing dissolved oil at an intermediate point thereof, removing oil phase rich in asphalt from said first zone, removing propane containing dissolved oil from said zone and recovering the oil therefrom as one product of the process; maintaining a second .body of liquid propane containing dissolved oil in a second treating zone, maintaining a second body of an oil phase rich in asphalt below said body of liquid propane containing dissolved oil in said second zone, said two bodies meeting at a common interface, introducing liquid propane into said second oil phase rich in asphalt, passing the removed oil phase rich in asphalt from the first zone into an intermediate point of the body of propane containing dissolved oil in said second zone, removing oil phase rich in asphalt from the second zone and passing a portion thereof into the first zone at the feed inlet level of said zone, recovering oil from the remainder of the removed oil phase rich in asphalt from the second zone as a second product of the process, withdrawing propane containing dissolved oil from the second zone and recovering the oil therefrom as a third product of the process.

2. The process of claim 1 wherein the top of the first zone is maintained at a temperature between the limits of 190 and 210 F., the lubrieating oil stock feed point is maintained at a temperature between the limits of 180 and 195 F., and the bottom of this zone is maintained at a temperature between the limits of 175 and 190 F., and said first zone is maintained under a pressure greater than the vapor pressure of propane at the highest temperature in said first zone; and wherein the top of the second zone is maintained at a temperature within the limits of 12 to 160 F., the bottom of said second zone is maintained at a temperature between the limits of 130 to F., the top of this second zone is maintained at a higher temperature than the bottom thereof at all times, and said second zone is maintained under a pressure greater than the vapor pressure of propane at the highest temperature in said second zone; and wherein the propane to crude oil ratio in the first zone is maintained between the limits of 6 to 1 and 10 to 1 and the ratio of the propane-to-oil in the second zone is maintained between the limits of 6to1and10t0l.

3. The process of claim 2 wherein the proportion of the oil-rich phase from the second zone introduced at the feed inlet level of the first zone is within the limits of 10% to 50% of the oil rich phase withdrawn from said second zone.

4. The process of claim 3 wherein the pressure maintained in the first zone is 649 pounds per square inch gage and the pressure maintained in the second zone is 460 pounds per square-inch gage.

5. In the propane fractionation of lubricating oil constituents fromlow asphalt-content reduced crude lubricating oil stocks with liquid propane wherein solid asphaltic material precipitates upon initial contact with the propane and adheres to and plugs the fractionating apparatus in the region adjacent and below the raw feed entry point, a process for continuously carrying out this-fractionation operation without precipitating said asphalt and plugging said apparatus comprising maintaining a body of liquid propane containing dissolved oil in a first treating zone, maintaining a body ofan oil phase rich in asphalt below said body of propane containing dissolved oil in said zone, said bodies meeting at a common interface, introducing a stream of liquid propane into said body of oil phase rich in asphalt and a stream of the asphalt-containing lubricating oil stock into said zone at an intermediate point thereof, removing oil phase rich in asphalt from said first zone, removing propane containing dissolved oil from said zone and recovering the oil therefrom as one product of the process; maintaining a second body of liquid propane containing dissolved oil in a second treating zone, maintaining a second body of an oil phase rich in asphalt below sa1d body of liquid propane containing dissolved oil in said second zone, said two bodies meeting at a common interface, introducing liquid propane into said second oil phase rich in asphalt, passing said removed o-il phase rich in asphalt from the first zone to anintermediate point of the bodi of propane containing dissolved oil in said second zone, removing oil phase rich in asphalt from the second zone and admixing a portion thereof with said stream of said asphalt-containing lubricating oil stock prior to its introduction into said first zone at said intermediate point, re covering oil-from the remainder of the removed oil phase rich in asphalt from the second zone as a second product of the process, withdrawing propane containing dissolved oil from the second zone and recovering the oil therefrom as a third product of the process.

6. The method of claim 5 wherein said cornmon interface in said first zone is maintained at a point below said intermediate point of said zone. f

7. The method of claim 6 wherein the top of 13. the first zone is maintained at a temperature between the limits of 190 and 210 F., the lubrieating oil stock feed point is maintained at a temperature between the limits of 180? and 195 F., and the bottom of this zone is maintainedat a temperature between the limits of 175 and 190 F. and said first zone is maintainedunder a preswherein the top of the second zone is maintained at a temperaturerwithin the limits of 140 to 160 F., the bottom of said second zone is maintained at a temperature between the limits of 130- to 150 the top of this second zone is maintained at a higher temperature than the bottom thereof at all times, and said second zone is maintained under a pressure greater than the vapor pressure of propane at the highest temperature in said second zone; and wherein the propane-to-crude oil ratio in the first zone is maintained between the limits of 6 to 1 and 10 to 1 and the ratio of the propane-to-oil in the second zone is maintained between the limits of 6 to 1 and 10 to 1.

8. The method of claim 7 wherein the proportion of the oil-rich phase from the second zone admixed with the lubricating oil stock and introduced at the midpoint of the first zone is within the limits of 10% to 50% of the oil-rich phase withdrawn from said second zone.

9. In the propane fractionation of lubricating oil constituents from low asphalt-content reduced crude lubricating oilstocks with liquid propane wherein solid asphalticmaterial precipitates upon initial contact with the propane and adheres to and plugs the fractionating apparatus in the region adjacent and below the raw feed entry point, a process for continuously carrying out this fractionation operation without precipitating said asphalt and plugging said apparatus comprising maintaining a body of liquid propane containing dissolved oil in a first treating zone, maintaining a body of an oil phase rich in asphalt below said body of propane containing dissolved oil and in said zone, said bodies meeting at a common interface, introducing a stream of liquid propane into said body of oil phase rich in asphalt and 'a stream of said asphalt-containing lubricating oil stock into said body of oil phase rich in asphalt at a midpoint of said zone, removing oil phase rich in asphalt from said first zone, removing propane containing dissolved oil from said zone and recovering the oil therefrom as one product of the process; maintaining a second body of liquid propane containing dissolved oil in a second treating zone, maintaining a second body of an oil phase rich in asphalt below said body of liquid propane containing dissolved oil and in said second zone, said two bodies meeting at a common interface, introducing liquid propane into said second oil phase rich in asphalt,

passing said removed oil phase rich in asphalt from the first zone into the midpoint of the body oil constituents from low asphalt-content reduced crude lubricating oil stocks with liquid propane wherein solid asphaltic material procipitates upon initial contact with the propane and adheres to and plugs the fractionatingapparatus in the region adjacent and below the raw feed entry point, a process for continuously carrying out this fractionation operation without precipitating said asphalt and pluggingsaid apparatus comprisin maintaining a body ofliquid propane containing dissolved oil in a first treating zone, maintaining a body of an oil phase rich in asphalt below said body of propane containing dissolved oil insaid zone, said bodies meeting'at a common interface, introducing-a'stlr'eam of liquid propane into said body of oil"phase rich in asphalt and a stream of said 'asphalt containing lubricating oil stool: into said body of liquidfpropane containing dissolved oil at an "intermediate point thereof, removing oil phase rich'in" asphalt from said'first zone, removing propane containing dissolved oil from said zone and recovering the oil therefrom as one product of the process; maintaining a second body of-liquid propane containing dissolved oil in a second treating zone, maintaining a second body of an oil-phase'rich in asphalt below said body of liquid propane containing dissolved oil in said second zone, said two bodies meeting at a common interface, introducing liquid propane into said second oil phase rich in asphalt, passing said removed oil phase rich in asphalt from the first zone into an intermediate point of the body of propane containing dissolved oil in said second zone, removing oil phase rich in asphalt from the second zone and passing a portion thereof into the first zone near the feed inlet level of said zone, recovering oil from the remainder of the removed oil phase rich in asphalt from the second zone as a second product of the process, withdrawing propane containing dissolved oil from the second zone and recovering the oil therefrom as a third product of the process.

11. In a process for the fractionation of a lubricating oil stock containing some asphalt with liquid propane wherein a deposit of asphalt is formed and adheres to and plugs the fractionating apparatus, a method for carrying out said fractionation without deposition of asphalt and plugging of the fractionation apparatus comprising maintaining a body of liquid propane containing dissolved oil in a first treating zone, maintaining a body of an oil-rich phase below said body of propane containing dissolved oil in said zone, said bodies meeting at a common interface, introducing a stream of liquid propane into said body of oil-rich phase and a stream of the asphalt-containing lubricating oil stock into said zone at an intermediate point thereof and below said common interface, removing oil-rich phase from said first zone, removing propane containing dissolved oil from said zone and recovering the oil therefrom as one product of the process; maintaining a second body of liquid propane containing dissolved oil in a second treating zone, maintaining a second body of an oil-rich phase below said body of liquid propane containing dissolved oil in said second zone, said two bodies meeting at a common interface, introducing liquid propane into said second oil-rich phase, passing said removed oil-rich phase from the first zone to an intermediate point of the body of propane containing dissolved oil in said second zone, removing oil-rich phase from the second zone and admixing a portion thereof with said stream of said asphalt-containing lubricating oil stock prior to its introduction into said first zone at said intermediate point, recovering oil from the remainder of the removed oil-rich phase from the secon zone as a second product of the process, withdrawing propane containing dissolved oil from the second zone and recovering the oil therefrom as a third product of the process.

12. The method of claim 11 wherein the top of the first zone is maintained at a temperature between the limits of 190 and 210 F., the lubrieating oil feed point is maintained at a temperature between the limits of 180 and 195 F.,i and the bottom of this zone is maintained at the same temperature as that of said feed point, and said first zone is maintained under a pressure greater than the vapor pressure of propane at the highest temperature in said first zone; and wherein the top of the second zone is maintained at a temperature within the limits of 140 to 166 F., the bottom of said second zone is maintained at a temperature between the limits of 130 to 150 F., the top of this second zone is maintained at a higher temperature than the bottom thereof at all times, and said second zone is maintained of propane at the highest temperature in said second zone; and wherein the propane-to-lubrieating oil stock ratio in the first zone is maintained between the limits of 6:1 and'lfltl and the ratio of the propane-to-lubricating oil stock in the second zone is maintained between the limits of 6:1 and 10:1.

13. The method of claim 12 wherein the proportion of the oil-rich phase from the second zone introduced at the feed inlet level of thefirst zone is within the limits of 10% to 50% of the oilrich phase withdrawn from said second zone.

14. The method of claim 12 wherein the pressure maintained in the first zone is 640 pounds per square inch gage and the pressure maintained in the second zone is %60 pounds per square gage.

BRUCE C. BENEDICT.

REFERENCES JFEED The following references are of record in the file or this patent:

UNITED STATES PATENTS Number Name Date 2,213,798 Anne -1 Sept. 3, 1940 2,367,385 Weeks et al Jan. 15, 1945 2,367,671 Dickinson et'al. Jan. 23, 1945 

5. IN THE PROPANE FRACTIONATION OF LUBRICATING OIL CONSTITUENTS FROM LOW ASPHALT-CONTENT REDUCED CRUDE LUBRICATING OIL STOCKS WITH LIQUID PROPANE WHEREIN SOLID ASPHALTIC MATERIAL PRECIPITATES UPON INITIAL CONTACT WITH THE PROPANE AND ADHERES TO SAID PLUGS THE FRACTIONATING APPARATUS IN THE REGION ADJACENT AND BELOW THE RAW FEED ENTRY POINT, A PROCESS FOR CONTINUOUSLY CARRYING OUT THIS FRACTIONATING OPERATION WITHOUT PRECIPITATING SAID ASPHALT AND PLUGGING SAID APPARATUS COMPRISING MAINTAINING A BODY OF LIQUID PROPANE CONTAINING DISSOLVED OIL IN A FIRST TREATING ZONE, MAINTAINING A BODY OF AN OIL PHASE RICH IN ASPHLAT BELOW SAID BODY OF PROPANE CONTAINING DISSOLVED OIL IN SAID ZONE,SAID BODIES MEETING AT A COMMON INTERFACE, INTRODUCING A STREAM OF LIQUID PROPANE INTO SAID BODY OF OIL PHASE RICH IN ASPHALT AND A STREAM OF THE ASPHALT-CONTAINING LUBRICATING OIL STOCK INTO SAID ZONE AT AN INTERMEDIATE POINT THEREOF, REMOVING OIL PHASE RICH IN ASPHALT FROM SAID FIRST ZONE, REMOVING PRPANE CONTAINING DISSOLVED OIL FROM SAID ZONE AND RECOVERING THE OIL THEREFROM AS ONE 